The U.S. solar industry is on edge, waiting to see whether the Trump administration will impose steep tariffs on foreign-made solar panels. Unease over the looming decision is already affecting the market. Will Stone of member station KJZZ in Phoenix reports that a trade commission is set to make its recommendations to the president in just a few days.

WILL STONE, BYLINE: To see just how far solar has come, take a climb to the top of parking structure number five in the heart of Arizona State University's campus. There are rows of solar panels and, every few minutes, a rising hum.

(SOUNDBITE OF TRACKER HUM)

LEE FELICIANO: That was the tracker moving two degrees to follow the path of the sun.

STONE: When Lee Feliciano developed this back in 2008, it was one of the biggest solar projects in Arizona. And these panels came at a premium. Since then, a lot has changed.

FELICIANO: Ninety percent decline in the price of the solar panels over less than 10 years. And part of that is due to volume. Part of that is due to an expanding global market and, really, the entry of China.

STONE: Cheap solar panels from Asia have led to a booming industry across the U.S. But now Feliciano, whose company invests in such projects, worries possible trade protections could so much as double the price of imported panels.

FELICIANO: This tariff could hit us within the next couple of months. And so there's that uncertainty right now with almost our entire pipeline.

STONE: This threat of a tariff started when two domestic manufacturers of solar panels lodged a complaint under U.S. trade law arguing the flood of imports has made it impossible for them to compete. Attorney Tim Brightbill represents one of those manufacturers, SolarWorld.

TIM BRIGHTBILL: In order to have a strong solar industry, you have to have a strong manufacturing industry.

BRIGHTBILL: Solar demand is going to continue to grow. Solar installations will grow.

STONE: But that's not what most of the industry believes. They say it would kill tens of thousands of jobs tied to installing solar, especially when it comes to building the largest facilities, known as utility-scale solar. That sector has grown nearly 70 percent each year since 2010.

MORTEN LUND: It's all a big math problem.

STONE: Morten Lund is a San Diego-based attorney who represents renewable energy developers and says if panels suddenly double in price...

LUND: That's a completely massive, game-changing increase. And so it's not something you can just casually plan around.

STONE: And the fate of such projects under a tariff could rest on which state they're planned for.

LUND: Where the big solar was or was about to be price-competitive with other types of electricity, it almost certainly will no longer be competitive at all.

STONE: But that all depends on what regulators recommend to President Donald Trump - a tariff, a quota or some combination - and then what he ultimately decides to do. Shayle Kann is the head of GTM Research.

SHAYLE KANN: The president has fairly wide leeway to implement whatever he so desires.

STONE: Given Trump's tough talk on China and support of tariffs in general, the solar market is now in turmoil as companies wait to see what happens. For NPR News, I'm Will Stone in Phoenix.